We propose to examine the joint toxic action of sulfur dioxide and ozone. Concentrations used will be in the range of 0.2 - 0.8 ppm of each gas. They will be combined in equal concentration as well as in varying ratios. The criteria of irritant response will be alterations in the respiratory mechanics of guinea pigs. The response of the combination will be compared to previously observed changes produced by sulfuric acid. We also plan to study the uptake of sulfur dioxide by wetted wall tubes with and without the addition of aerosols. We plan to study the solubility and reactivity of sulfur dioxide in solutions of various salt which have been shown to potentiate the biological response.